Using organic fertilisers in growing media for young plant production

Organic fertilisers are used more and more in growing media. Often this causes plant damage because the different behavior when compared with mineral fertilisers are not foreseen. Especially mineralisation of organic nitrogen can cause damage to plants. Mineralisation of organically bound nitrogen happens because of bacteria in a dynamic process that inhabits ammonification and nitrification. The course of this process is mainly depending on presence of nitrifying bacteria and the right pH. A lack of nitrifying bacteria can lead to increasing levels of ammonium can - depending on the pH - dissociate to levels of ammonia harmful for plants. This can be aggravated by a low pH buffering and/or a high initial pH value of the growing medium. Growing trials with lettuce and turnip cabbage on various growing media did show that germinating seeds suffer of inhibition of germination and growth when they meet the stage of the mineralization process of the organic fertiliser where ammonia does appear. When using organic fertilisers in growing media for young plant production it is of major importance that a growing medium does support the mineralisation process and that exposure of the crop to an exceeding ammonia level is prevented.